This actually took me quite a bit of thinking, which I imagine means that it was good for me. I'm a rather bookish person, and so most of my biggest influences are authors or books. For good or ill, most of the greatest influences in my life (beyond my wife and immediate family) are books, not people.
The Top Ten Influences (excluding God and family) Meme (inflicted by Pro Ecclesia and Fr. Martin Fox)
These start out in chronological order and then are just in any old order at all.
1. I'm going to break the family rule right off, because this does deserve a place. Arguably the single greatest influence on my life was my youngest brother, Jonathon, who died of SIDS on the morning of Epiphany when I was seven. It is fairly rare these days for a child of seven to experience the reality that death can come at any time to any person -- even someone younger than himself. Some people don't seem to hit that realization till they're in their forties... I think it also probably pushed me hard in the direction of self sufficiency from a young age. In a family tragedy like that, your parents certainly provide lots of support and comfort, but at the same time you can sense that they have their own sorrow to deal with.
2. Greek & Norse Mythology -- I still have on the shelf the copy of Gods & Heroes from Viking Mythology by Brian Branston which I was given for my fifth birthday. This and a similar large illustrated book of Greek mythology were standard read-alouds in my family as far back as I can remember. Looking back, I think one of the things I got from hearing so much pagan mythology at a young age was that often fate deals you lousy cards, and heroism consists of dealing well with a bad situation. I don't "believe in fate" the way people do when they say that something is "meant to happen", but I certainly believe that there is no guarantee that you will be as happy as you want to be in life. Sometimes we're placed in situations (see above) where the best you can do is suffer well.
3. The NRA -- For my tenth birthday, I desperately wanted an air rifle. The ruling was that if I checked out enough books from the library to fully understand gun function and safety that I could have one -- with the understanding that if I ever violated these safety rules I would lose the air rifle. By age ten, I was already a voracious reader, so once I got started reading about guns, I didn't really stop. Before long I got into reading American Rifleman (the NRA's magazine) every month at the library. The NRA's second amendment advocacy and somewhat libertarian approach to conservatism was in many way the first introduction to American politics. The NRA certainly didn't remain my primary interest in politics (In fact, although I now own several guns I've never become a member.) and I quickly got into listening to conservative talk radio and such instead, but it was the beginning.
4. Plato -- I first encountered Plato in the Great Books based high school curriculum my parents put me through, and read him again in my college honors program and in various classics and philosophy classes. Certain of Plato's arguments, like the argument in Euthyphro for the existence of the ideal "good" and "justice" (which, as Aquinas would point out, is what we mean by "God") have become central to my faith. The dialogue form also made a great impression on me. And some of Plato's images (such as the cave in Republic) are hauntingly memorable and seem to sum up much of out intellectual predicament on this earth.
5. Tolkien -- I've read all of Tolkien's major works numerous times, and his imagery is very much part of my intellectual and artistic vocabulary. However The Hobbit and Lord of the Rings are probably not the biggest influences on me, though I love both and have read them a number of times. The Silmarillion is a truly brilliant synthesis of Christian imagery expressed through the medium of pagan myth. My father must have read the creation story from the Silmarillion to me at a very young age, because for years I actually thought it was part of the Bible. My other favorite Tolkien work is The Smith of Wooten Major, a story which I have (I can't say why) always associated with death and the afterlife.
6. Waugh -- Brideshead Revisited is easily one of the single most influential books in my life. I've read it numerous times, and many of its themes have molded my relationship with and understanding of Catholicism.
7. Stephen Jay Gould -- In case no on has noticed, evolution evolution is one of my interests... Gould is not a brilliant writer by any stretch, though his popular books and collections of essays are well worth reading a show a wide ranging set of intellectual interests. One particular essay of his, however, have very much stayed with me: his piece on Nonoverlapping Magisteria, which he later expanded into the book Rocks of Ages. Gould doesn't fully understand the concept of a world with multiple levels of meaning, but for an atheist he does a good and very honest job of trying to give both religion and science their own separate and important spheres, and explain the differences between these two types knowledge. It's far from perfect, but it's noble and under-appreciated effort.
8. John Paul II -- I was born during the first year of John Paul II's pontificate, so it goes without saying that he in many ways defines the modern papacy for me. While the importance of the papacy is the protection from error which Christ promised Peter and his successors, at the human level it must have been very different to experience Paul VI's reign during one's formative years rather than John Paul II's. However, it's not the World Youth Day "rock star" side of John Paul II's papacy that strongly affected me, but rather his personalist philosophy as applied to the question of human sexuality. Love and Responsibility (which I've read twice) and Theology of the Body (which I keep trying to read but stalling out on) lay out an understanding of sexuality that takes the Church's historical understanding of the human person and runs with it to produce a much more sophisticated set of sexual ethics than found in Aquinas or Augustine.
9. Dante -- I've read the Divine Comedy three times now, though I know I would benefit from doing so again. There is no greater work of Catholic literature. To follow it, a decent set of commentary is needed, especially the first time through. My own favorite by a long way is Dorothy Sayers' translation and commentary. Don't just stop with the Inferno either. The Purgatorio is arguably the best volume, and the Paradiso is also well worth reading. Nor should Dante be seen as the nasty old medieval condemning people to hell. The thing people forget is that the Divine Comedy is first and foremost an account of Dante's own conversion from sin to repentance and thence to grace.
10. Origen -- I read Origen in Stuebenville's great books based Honors Program. Nearly everyone else in the class hated him -- writing him off as a heretic. For me, he was possibly the most interesting of the early fathers. I read his Commentary on the Song of Songs and On First Principles. On First Principles is interesting, but it was the Commentary that really fascinated me. This was my first encounter with biblical criticism that went beyond what the author meant, indeed to meanings which the author could most certainly not have meant. Here, within two hundred years of the time of Christ and long before Constantine or the Council of nice, we find a well formed understanding of the multiple sense of scripture and a very sophisticated melding of ancient pagan thought with Christian theology -- though given the early date of origin's work, some of his conclusions (especially in On First Principles) would later be deemed article. Reading Aquinas and Augustine during high school, I hadn't seen theology and biblical criticism in particular as being as imaginative as Origen made it. Certainly, Aquinas states (more clearly than Origen) the four senses of scripture. Reading Origen, however, made me understand what interpreting scripture at different levels actually looked like.
And there it is.
I hesitate to "tag" anyone, being a self professed non-lover of memes, but I'd be really curious to see Erin of Bearing Blog, Bernard of A Little Light from the East, and Michael of Sacramentum Vitae list their top ten influences.